Mobile communication terminal supporting multi-modal communications and methods for providing seamless service upon handover to the mobile communication terminal

ABSTRACT

A method of providing a handover service to a mobile communication terminal supporting multi-modal communications, and a mobile communication terminal for performing the method are provided. More particularly, a method of eliminating an interruption of a data transmission service occurring during a handover between different communication networks, and a terminal for performing the method are provided. A method of providing a handover service of a mobile communication terminal supporting multi-modal communications can include: transmitting and receiving data to/from a corresponding node via a first access network and a second access network while simultaneously maintaining an association with the first access network and the second access network, determining a point in time of completing a handover registration, and releasing an association with the first access network after the point in time of completing the handover registration.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. patent application Ser. No.11/797,269 filed on May 2, 2007, now allowed, which claims the benefitof Korean Patent Application No. 10-2006-0096313 filed on Sep. 29, 2006,in the Korean Intellectual Property Office, the disclosure of which isincorporated herein by reference in its entirety

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method of providing a handoverservice to a mobile communication terminal that is capable ofmulti-modal communication, and a mobile communication terminal forperforming the method. More particularly, the present invention relatesto method of eliminating an interruption of a data transmission serviceoccurring during a handover between different communication networks,and a mobile communication terminal for performing the method.

2. Description of Related Art

Developments in wireless communication networks currently create a needfor constant development of communication networks. Differentcommunication networks with diverse characteristics, such as acellular-based mobile communication network starting from an analogmethod and developing to a digital method, a wireless broadband Internet(WiBro) communication network providing a high-speed data service, awireless local area network (WLAN), a wireless private area network, andthe like are overlapping, and provide users with more diversecommunication services.

Also, a mobile communication terminal constantly and functionallydevelops along with developments of the communication networks, andaccordingly may provide diverse services in each similar communicationnetwork. Also, a multi-modal mobile communication terminal providing aservice in the different communication networks is developing. Amulti-modal terminal has a plurality of wireless interfaces, and aconnection capability with various wireless communication networks.

A vertical handover (VHO) process from a first communication network toanother communication network is required so that the multi-modal mobilecommunication terminal may smoothly provide service during a transitionbetween the different communication networks. However, sincecommunication network characteristics such as load, transmissionenvironment, system, and the like, vary according to each communicationnetwork, a communication disconnection occurring during a handover maycause more complex and serious problems than in a single communicationnetwork.

FIGS. 1 through 4 are diagrams illustrating existing handover processesbetween different wireless communication networks.

Since a multi-mode mobile node (MN) includes at least one interface, theMN implements communication by connecting with a wireless communicationnetwork corresponding to a mode for each interface.

Referring to FIG. 1, the MN connects with a first wireless accessnetwork (AN1), and connects with a corresponding node (CN) via a firstbackbone network (BN1).

In this instance, a need for a VHO from a present wireless communicationnetwork to another wireless communication network may be generated dueto diverse reasons. As an example, a handover may occur when the MN isremoved from a region being covered by the AN1 to a region being coveredby a second access network (AN2) as in a case of changing the MN'slocation, or when switching to another wireless communication network isrequired to control power usage of the MN. Another instance is when anappropriate communication network is selected according to the type ofuser-desired communication service, and a handover to a selectedcommunication network is required.

As illustrated in FIG. 2, when a MN determines a handover from the AN1to the AN2, the MN releases an association with the AN1, and transmits arequest message for a handover registration via the AN2. The requestmessage for the handover registration may include MN identificationinformation identifying the MN, MN location information (for example, anInternet Protocol (IP) address), and the like, and is used as a messagefor the MN to register variations to an individual's location in anetwork. FIG. 2 illustrates a binding update message (BU) according to astandard of a mobile IP as an example of the request message for thehandover registration.

A request message for a handover registration is transmitted (referringto FIG. 3) to a CN via a second backbone network (BN2), and the CNtransmits a response message (referring to FIG. 4) to a request for thehandover registration, i.e. a BU acknowledgement (BU_ACK) to an MN viaan AN2, and thereby informs the MN that the CN normally identifies (orreceives) the request for the handover of the MN. FIG. 4 illustrates aBU_ACK according to a mobile IP standard as an example of a responsemessage to the request for the handover registration.

As illustrated in FIGS. 2 and 3, while the MN determines the handoverand a request message for the handover registration is transmitted tothe CN via the AN2 and the BN2, the CN transmits data through the BN1and the AN1. Accordingly, this method does not allow the datatransmitted via the AN1 to be received at the MN and is lost.

FIG. 5 is a diagram illustrating a flow of transmitting and receiving amessage related to a handover between a CN and an MN according to aperiod of time, according to an existing method.

Referring to FIG. 5, the CN transmits data, while maintaining anassociation with a first interface (IF1) of the MN in time t0. When thehandover is determined, the MN switches an association from an AN1 to anAN2 in time t1. In this instance, a second interface (IF2) transmits arequest message for a handover registration (BU) to the CN via the AN2.In time t2, the CN receives the request message for the handoverregistration (BU) and stops data transmission to the IF1. Also, aresponse message to a request for the handover registration (BU_ACK) istransmitted to the IF2 via the AN2 in response to receiving the requestmessage for the handover registration. The IF2 of the MN receives theresponse message to the request for the handover registration (BU_ACK)in time t3.

In FIG. 5, before the CN receives the request message for the handoverregistration (BU) from the MN, i.e. before time t2, the CN continuouslytransmits the data to the IF1 via the AN1. Accordingly, from a point intime when the MN determines the handover to a point in time when the CNreceives the request message for the handover registration (BU), i.e.for a period of time of t0-t2, the MN may lose the data transmitted fromthe CN via the AN1.

As a conventional art to restore the data of a period of time of t0-t2,an existing method buffers and then forwards the data (a packet)transmitted from the CN to a node existing in the AN1 (for example, anaccess point (AP) or a router). Thus, the method is disadvantageous inthat an additional function supporting the VHO is required to embody inthe communication network.

Accordingly, a need exists for new technology to solve the problems ofthe conventional art in the process of performing a handover in anenvironment where different communication networks are distributed, andefficiently provide for seamless data service.

SUMMARY OF THE INVENTION

An aspect of exemplary embodiments of the present invention is toaddress at least the above problems and/or disadvantages and to provideat least the advantages described below. Accordingly, an aspect ofexemplary embodiments of the present invention is to provide a method ofproviding a handover service to a mobile communication terminalsupporting multi-modal communications, and a mobile communicationterminal for performing the method to voluntarily prevent datainterruption, eliminating assistance from a communication network duringa handover.

An aspect of exemplary embodiments of the present invention alsoprovides a method of providing a handover service to a mobilecommunication terminal supporting multi-modal communications, and amobile communication terminal for performing the method where a load,due to tunnel maintenance and packet transmission, in a communicationnetwork can be reduced, and may allow a mobile communication terminal tosmoothly implement a handover.

An aspect of exemplary embodiments of the present invention alsoprovides a method of a handover service for a mobile communicationterminal capable of multi-modal communication, and a mobilecommunication terminal for performing a method allowing a packet to besmoothly received by eliminating the problem of having to reorderpackets a terminal receives during the process of a handover.

An aspect of exemplary embodiments of the present invention alsoprovides a method of providing a handover service to a mobilecommunication terminal that is capable of multi-modal communication, anda mobile communication terminal for performing the method which mayallow a seamless service to be efficiently provided, eliminating theneed for additional devices by advantageously using the multi-modalfunction in the terminal.

According to an exemplary embodiment of the present invention, there isprovided a method of providing a handover service to a mobilecommunication terminal capable of multi-modal communication, the methodincluding: transmitting and receiving data to/from a corresponding nodevia a first access network and a second access network whilesimultaneously maintaining an association with the first access networkand the second access network; determining a point in time of completinga handover registration; and releasing an association with the firstaccess network after the point in time of completing the handoverregistration.

According to another exemplary embodiment of the present invention,there is also provided a method of providing a handover service to amobile communication terminal capable of multi-modal communication, themethod including: transmitting and receiving data to/from acorresponding node via a first access network and a second accessnetwork while simultaneously maintaining an association with the firstaccess network and the second access network; transmitting a requestmessage for the handover registration to the corresponding node via thesecond access network; receiving, via the first access network, aresponse message from the corresponding node sent in response toreceiving the request message for the handover registration; andreleasing an association with the first access network after receivingthe response message to the request for the handover registration.

According to still another exemplary embodiment of the presentinvention, there is provided a method of providing a handover service toa mobile communication terminal capable of multi-modal communication,the method including: transmitting and receiving data to/from acorresponding node via a first access network and a second accessnetwork while simultaneously maintaining an association with the firstaccess network and the second access network; transmitting a requestmessage for the handover registration to the corresponding node via thesecond access network; receiving, via the second access network, aresponse message to a request for the handover registration from thecorresponding node; receiving, via the first access network, acompletion message of the handover registration from the correspondingnode in response to receiving the request message for the handoverregistration; and releasing an association with the first access networkafter receiving the completion message of the handover registration.

According to yet another exemplary embodiment of the present invention,there is provided a method of providing a handover service to a mobilecommunication terminal capable of multi-modal communication, the methodincluding: transmitting and receiving data to/from a corresponding nodevia a first access network and a second access network whilesimultaneously maintaining an association with the first access networkand the second access network; calculating a first estimated period oftime when a response message to a request for the handover registrationis transmitted from the corresponding node to the mobile communicationterminal via the first access network; calculating a second estimatedperiod of time when a request message for the handover registration istransmitted from the mobile communication terminal to the correspondingnode via the second access network; determining the point in time ofcompleting the handover registration according to the first estimatedperiod of time and the second estimated period of time; and releasing anassociation with the first access network after the point in time ofcompleting the handover registration.

Other objects, advantages, and salient features of the invention willbecome apparent to those skilled in the art from the following detaileddescription, which, taken in conjunction with the annexed drawings,discloses exemplary embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features, and advantages of certainexemplary embodiments of the present invention will be more apparentfrom the following detailed description, taken in conjunction with theaccompanying drawings in which:

FIGS. 1 through 4 are diagrams illustrating handover processes betweendifferent wireless communication networks according to conventionalarts;

FIG. 5 is a diagram illustrating a flow of transmitting and receiving amessage related to a handover between a corresponding node (CN) and amulti-mode mobile node (MN) according to a period of time, according tothe conventional arts;

FIG. 6 is a flowchart illustrating a method of providing a handoverservice according to an exemplary embodiment of the present invention;

FIG. 7 is a diagram illustrating a process of receiving a message from aCN to determine a point in time of completing a handover registrationaccording to an exemplary embodiment of the present invention;

FIG. 8 is a flowchart illustrating a flow to determine a point in timeof completing a handover registration according to an exemplaryembodiment of the present invention;

FIG. 9 is a diagram illustrating a process receiving a message from a CNto determine a point in time of completing a handover registrationaccording to another exemplary embodiment of the present invention;

FIG. 10 is a diagram illustrating a method of estimating a period oftime when it is required that a terminal voluntarily maintains anassociation with a first access network (AN1) to determine a point intime of completing a handover registration according to anotherexemplary embodiment of the present invention;

FIG. 11 is a flowchart illustrating a method of providing a handoverservice according to another exemplary embodiment of the presentinvention; and

FIG. 12 is a block diagram illustrating a mobile communication terminalsupporting multi-modal communications according to an exemplaryembodiment of the present invention.

Throughout the drawings, the same drawing reference numerals will beunderstood to refer to the same elements, features, and structures.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

The matters defined in the description such as a detailed constructionand elements are provided to assist in a comprehensive understanding ofthe embodiments of the invention. Accordingly, those of ordinary skillin the art will recognize that various changes and modifications of theembodiments described herein can be made without departing from thescope and spirit of the invention. Also, descriptions of well-knownfunctions and constructions are omitted for clarity and conciseness.

Hereinafter, a method of providing a handover service and a mobilecommunication terminal for performing the method according to theexemplary embodiments of the present invention will be described withreference to the attached drawings.

The mobile communication terminal according to the exemplary embodimentsof the present invention provides a terminal with mobility and, moregenerally, provides a mobile node. The mobile communication terminal isunderstood to be a comprehensive definition including a deviceimplementing a communication with a counterpart node (or correspondingnode) by connecting with different access networks.

A corresponding node (CN) (or a counterpart node) used in accordancewith an exemplary embodiment of the present specification indicates anode implementing a communication service connecting with the mobilecommunication terminal via a plurality of wireless communicationnetworks, and shall be understood to be a comprehensive definitionincluding all devices with communication interfaces directly connectingwith a wired/wireless communication network.

An association used in the present invention is understood to be astatus indicating that a terminal (or a node) may transmit and receivedata by connecting with the communication network, and shall beunderstood to comprise meanings such as a connection, a linkage, and thelike.

An access network used in the present invention is understood to be avertical section in the communication network directly connecting withthe terminal, may be applied to diverse wireless communication networkssuch as a mobile communication network, a wireless broadband Internet(WiBro) communication network, a wireless local area network (WLAN), awireless private area network, and the like, and is not limited to anyone of communication networks.

FIG. 6 is a flowchart illustrating a method of providing a handoverservice according to an exemplary embodiment of the present invention.Hereinafter, a function implemented in each operation will be describedin detail with reference to FIG. 6.

First, in operation S610, the terminal transmits and receives datato/from a corresponding node via a first access network (AN1) and asecond access network (AN2) while simultaneously maintaining anassociation with the first access network and the second access network.

The mobile communication terminal according to an exemplary embodimentof the present invention is a terminal that supports multi-modalcommunications, and may transmit and receive data, while simultaneouslymaintaining the association with at least two wireless access networks.Accordingly, the terminal may continuously maintain the association withan existing access network (AN1) until a point in time when the terminalreceives the data via the access network (AN1), while simultaneouslymaintaining a new association with an access network (AN2).

In operation S620, a point in time of completing the handoverregistration is determined. According to an exemplary embodiment of thepresent invention, the terminal is preferably required to continuouslymaintain the association with the AN1 to continuously receive datatransmitted from the CN without loss after transmitting a requestmessage for the handover registration. However, since the associationwith the AN1 may not be indefinitely maintained for a vertical handover(VHO), the terminal is preferably required to identify a point in timeuntil which the association with the AN1 is maintained, in order toprevent data loss. Accordingly, in operation S620, a point in time untilwhich the association with the AN1 is maintained is determined bydeciding a point in time when the handover registration is completed.

Next, in operation S630, after the point in time of completing thehandover registration has passed, the association with the AN1 isreleased.

A few exemplary embodiments of the present invention for determining apoint of time of completing the handover registration are described. Asan example, there is provided a method by receiving assistance from theCN where the CN informs the terminal of a point in time when the datatransmitted to the existing access network is completed. As anotherexample, there is provided a method of estimating a minimum period oftime when the terminal is required to voluntarily maintain theassociation with the AN1 and releasing the association after anestimated period of time.

FIG. 7 is a diagram illustrating a process of receiving a message from aCN to determine a point in time of completing a handover registrationaccording to an exemplary embodiment of the present invention.Hereinafter, a process of receiving a message will be described indetail with reference to a flowchart of FIG. 8.

In operation S810 of FIG. 8, the terminal transmits a request messagefor the handover registration to the CN via the AN2.

Next, in operation S820, the CN transmits a completion message of thehandover registration, i.e. a binding update acknowledgement (BU_ACK),to the mobile communication terminal via the AN1 in response toreceiving the request message for the handover registration, asillustrated in FIG. 7. According to related art in FIG. 4, when the CNreceives the request message for the handover registration, the CNtransmits the response message to the terminal again, and therebyenables the terminal to confirm that the CN receives the request of thehandover registration of the terminal. In this instance, the accessnetwork where the response message is transmitted is the same accessnetwork, AN2 where the request for the handover registration isreceived.

However, according to the exemplary embodiment of the present invention,the terminal may interpret the complete message of the handoverregistration as a new and significant message in relation to the AN1 byusing not the AN2 but the AN1 when transmitting the response message tothe request for the handover registration. Similar to the descriptionabove, since the mobile communication terminal according to an exemplaryembodiment of the present invention may simultaneously maintain theassociation with the AN1 after establishing a new association with theAN2, the response message may be received via the AN1, and accordinglythe terminal may interpret the complete message as the new andsignificant message.

According to related art, the terminal may not know a point in time ofcompleting the data transmitted to the existing access network (AN1). Bycontrast and according to an exemplary embodiment of the presentinvention, the terminal may receive the response message from the AN1,and determine a point in time of receiving the response message from theAN1 as a point in time of completing the data transmitted from the AN1.Specifically, a point in time of receiving a completion message of thehandover registration is determined as a point in time of completing thehandover registration (S830).

In the exemplary embodiment of FIG. 8, the response message transmittedfrom the CN according to related art is newly defined as the completemessage, and is used for determining a point in time of completing thehandover registration.

However, according to the exemplary embodiment of FIG. 8, there is aproblem with the standards concerning transmission of the responsemessages being required to change in an existing handover protocol.

Accordingly, as another exemplary embodiment of the present invention,FIG. 9 defines a new message different from a conventional responsemessage to a request for the handover registration unlike FIG. 8, anduses the new message as the completion message.

According to the other exemplary embodiment of the present invention,the terminal receives the response message (BU_ACK) from the CN via theAN2 similar to related art. However, the CN additionally transmits acompletion message of the handover registration (BU_C) from the CN tothe terminal via the AN1 in response to receiving the request messagefor the handover registration transmitted from the terminal. Theterminal releases the association with the AN1 after receiving the BU_C.

FIG. 10 is a diagram illustrating a method of estimating a period oftime when it is required that a terminal voluntarily maintains anassociation with a first access network (AN1) to determine a point intime of completing a handover registration according to anotherexemplary embodiment of the present invention. FIG. 10 generally followsa message transmission (t1, t2 and t3) of FIG. 5, but t4 indicates apoint in time when a BU_C is received from the CN to the IF1 of theterminal.

According to the exemplary embodiment of the present invention, sincethe terminal may not know a point in time of completing the datatransmitted for the existing access network (AN1), time t4 is estimatedand used.

Specifically, as illustrated in FIG. 10, when the terminal releases(disconnects) the association with the IF1 and the AN1 in time t1 whenthe terminal determines the handover, the data transmitted from the CNto the IF1 between time t1 and time t4 is lost. Accordingly, to preventdata loss, the association with the IF1 and the AN1 is required to bemaintained for a longer period of time than the estimated period oftime, estimating a period of time between time t1 and time t4.

An equation may be drawn from the flowchart of FIG. 10, as follows.t4−t1=tn+tp  [Equation 1]

By using Equation 1, a method of providing a handover service accordingto still another exemplary embodiment of the present invention will bedescribed with reference to a flowchart of FIG. 11.

In operation S1110, data is transmitted and received to/from a CN via anAN1 and an AN2 while simultaneously maintaining an association with theAN1 and the AN2.

Next, in operation S1120, a first estimated period of time when aresponse message to a request for the handover registration istransmitted from the CN to the mobile communication terminal via the AN1is calculated. The terminal may calculate an amount of time for around-trip transmission of the packet until the terminal transmits arequest packet for the handover registration via the AN1, and receives aresponse packet to a request for the handover registration from the CNvia the AN1 while simultaneously maintaining the association with theAN1 via the IF1, and use half of a calculated value as a first estimatedperiod of time (tp).

Next, in operation S1130, a second estimated period of time when arequest message for the handover registration is transmitted from themobile communication terminal to the CN via the AN2 is calculated. Theterminal may calculate a period of a round-trip transmission time of thepacket until the terminal transmits a request packet for the handoverregistration via the AN2, and receives a response packet to a requestfor the handover registration from the CN via the AN2 whilesimultaneously maintaining the association with the AN2 via the IF2),and use half of a calculated value as a second estimated period of time(tn).

In operation S1140, the point in time of completing the handoverregistration according to the first estimated period of time and thesecond estimated period of time is determined In operation S1150, theassociation with the AN1 is released after the point in time ofcompleting the handover registration.

Calculation values of the first estimated period of time and the secondestimated period of time may be modified according to characteristics ofwireless communication networks and loads of communication networks.

An operation of determining the point in time of completing the handoverregistration (S1140) may determine the point in time of completing thehandover registration, wherein the point in time of completing thehandover registration (t4) is the addition of the first estimated periodof time and the second estimated period of time. The point in time (t1)of transmitting the request message to the CN via the AN1 is establishedas a starting point in time.

As still another exemplary embodiment of the present invention, whendetermining the point in time of completing the handover registration,the first estimated period of time and the second estimated period oftime may be added including a small margin. Specifically, byestablishing the margin along with the addition, the terminal maysufficiently maintain the association with the AN1, and receive the datatransmitted from a first CN (CN1) via the AN1 without loss.

According to the exemplary embodiments of the present inventiondescribed with reference to FIG. 10 and FIG. 11, since an estimatedvalue calculated in the terminal is used, there is an advantage that anadditional mechanism is not required for the CN and the communicationnetwork, and embodiments may be simply realized.

A method of providing a handover service of a mobile communicationterminal according to the above-described embodiment of the presentinvention may be recorded in computer-readable media including programinstructions to implement various operations embodied by a computer. Themedia may also include, alone or in combination with the programinstructions, data files, data structures, and the like. The media andprogram instructions may be those specially designed and constructed forthe purposes of the present invention, or they may be of the kindwell-known and available to those having skill in the computer softwarearts. Examples of computer-readable media include, but are not limitedto, magnetic media such as hard disks, floppy disks, and magnetic tape;optical media such as CD ROM disks and DVD; magneto-optical media suchas optical disks; hardware devices that are specially configured tostore and perform program instructions, such as read-only memory (ROM),random access memory (RAM), flash memory; and carrier waves (such asdata transmission through the Internet via wired or wirelesstransmission paths), and the like. The computer-readable recording mediacan also be distributed over network-coupled computer systems so thatthe computer-readable code is stored and executed in a distributedfashion. Also, functional programs, codes, and code segments foraccomplishing the present invention can be easily construed as withinthe scope of the invention by programmers skilled in the art to whichthe present invention pertains. Examples of program instructions includeboth machine code, such as produced by a compiler, and files containinghigher level code that may be executed by the computer using aninterpreter. The described hardware devices may be configured to act asone or more software modules in order to perform the operations of theabove-described embodiments of the present invention.

FIG. 12 is a block diagram illustrating a mobile communication terminal1200 supporting multi-modal communications according to an exemplaryembodiment of the present invention. Hereinafter, a function will bedescribed in detail for each configuring element with reference to FIG.12.

The mobile communication terminal according to an exemplary embodimentof the present invention may include at least one interface to connectwith a plurality of different communication networks, and transmit andreceive data according to each communication mode connecting with acorresponding communication network for each interface.

A first interface unit 1210 in FIG. 12 communicates with a CN on a firstcommunication mode while maintaining an association with an AN1), and asecond interface unit 1220 communicates with a CN on a secondcommunication mode while maintaining an association with an AN2.

A handover determining unit 1230 determines a point in time ofcompleting a handover registration from the AN1 to the AN2, and anassociation control unit 1240 controls the first interface unit torelease the association with the AN1 after the point in time ofcompleting the handover registration.

As an example for determining a point in time of completing a handoverregistration, when the second interface unit 1220 transmits a requestmessage for the handover registration to the CN via the AN2, and thefirst interface unit 1210 receives a completion message of the handoverregistration from the CN via the AN1, the handover determining unit 1230may determine a point in time of receiving the completion message of thehandover registration as the point in time of completing the handoverregistration.

As still another example according to the present invention, when thesecond interface unit 1220 transmits a request message for the handoverregistration to the CN via the AN2, and receives a response message to arequest for the handover registration from the CN via the AN2, the firstinterface unit 1210 receives a completion message of the handoverregistration from the CN via the AN1. The handover determining unit 1230may determine a point in time of receiving the completion message of thehandover registration as the point in time of completing the handoverregistration.

As another example according to the present invention, The handoverdetermining unit 1230 calculates a first estimated period of time when aresponse message to a request for the handover registration istransmitted from the CN to the mobile communication terminal via theAN1, calculates a second estimated period of time when a request messagefor the handover registration is transmitted from the mobilecommunication terminal to the CN via the AN2, and may determine thepoint in time of completing the handover registration according to thefirst estimated period of time and the second estimated period of time.Specifically, the handover determining unit 1230 may determine a pointin time as the point in time of completing the handover registration,wherein the point in time of completing the handover is after anaddition of the first estimated period of time and the second estimatedperiod of time, and a point in time of transmitting the request messageto the CN via the AN1 is established as a starting point in time.

Since the exemplary embodiment of a configuration of the mobilecommunication terminal supporting multi-modal communications accordingto the present invention is described, and technical contents describedin a method of providing a handover service in FIGS. 6 through 11 may beapplied to the exemplary embodiment of the present invention, thus, amore specific description is omitted.

According to the exemplary embodiments of the present invention, it ispossible to provide a seamless service eliminating data interruptionduring a handover between different communication networks.

According to the exemplary embodiments of the present invention, it ispossible that a load, due to tunnel maintenance and a packettransmission, in a communication network can be reduced, and can enablea mobile communication terminal to smoothly implement a handover.

According to the exemplary embodiments of the present invention, thereis an advantage that an additional mechanism is not required for the CNand the communication network, and embodiments may be simply made in atechnical method when providing a handover by using estimation.

According to the exemplary embodiments of the present invention, it ispossible to solve a reordering problem of received packets, since apacket buffering process is not required for restoring lost packets lostaccording to conventional art.

According to the exemplary embodiments of the present invention, it ispossible that a seamless service can be efficiently provided eliminatinga need for an additional device by using an advantage of a multi-modalfunction in the terminal.

While the invention has shown and described with reference to certainexemplary embodiments thereof, it will be understood by those skilled inthe art that various changes in form and details may be made thereinwithout departing from the spirit and scope of the invention as definedby the appended claims and their equivalents.

What is claimed is:
 1. A method of providing a handover service to amobile communication terminal supporting multi-modal communications, themethod comprising: transmitting and receiving data to/from acorresponding node via a first access network and a second accessnetwork, while simultaneously maintaining an association with the firstaccess network and the second access network; determining a point intime of completing a handover registration; and releasing an associationwith the first access network after the point in time of completing thehandover registration, wherein the determining comprises transmitting arequest message for the handover registration to the corresponding nodevia the second access network, receiving, via the first access network,a completion message of the handover registration from the correspondingnode in response to receiving the request message for the handoverregistration, and determining the point in time of receiving thecompletion message of the handover registration as the substantiallysame point in time of completing the handover registration.
 2. Themethod of claim 1, wherein the completion message of the handoverregistration is different from a response message which thecorresponding node transmits to the mobile communication terminal viathe second access network in response to receiving the request messagefor the handover registration.
 3. The method of claim 1, wherein thedetermining determines the point in time of completing the handoverregistration according to a first estimated period of time when aresponse message to a request for the handover registration istransmitted from the corresponding node to the mobile communicationterminal via the first access network, and a second estimated period oftime when a request message for the handover registration is transmittedfrom the mobile communication terminal to the corresponding node via thesecond access network.
 4. A method of providing a handover service to amobile communication terminal supporting multi-modal communications, themethod comprising: transmitting and receiving data to/from acorresponding node via a first access network and a second accessnetwork while simultaneously maintaining an association with the firstaccess network and the second access network; transmitting a requestmessage for the handover registration to the corresponding node via thesecond access network; receiving, via the first access network, aresponse message to the request for the handover registration from thecorresponding node in response to receiving the request message for thehandover registration; and releasing an association with the firstaccess network after receiving the response message to the request forthe handover registration.
 5. A method of providing a handover serviceof a mobile communication terminal supporting multi-modalcommunications, the method comprising: transmitting and receiving datato/from a corresponding node via a first access network and a secondaccess network while simultaneously maintaining an association with thefirst access network and the second access network; transmitting arequest message for the handover registration to the corresponding nodevia the second access network; receiving, via the second access network,a response message from the corresponding node in response to receivingthe request message for the handover registration; receiving, via thefirst access network, a completion message of the handover registrationfrom the corresponding node in response to receiving the request messagefor the handover registration; and releasing an association with thefirst access network after receiving the completion message of thehandover registration.
 6. A method of providing a handover service to amobile communication terminal supporting multi-modal communications, themethod comprising: transmitting and receiving data to/from acorresponding node via a first access network and a second accessnetwork while simultaneously maintaining an association with the firstaccess network and the second access network; calculating a firstestimated period of time when a response message to a request for thehandover registration is transmitted from the corresponding node to themobile communication terminal via the first access network; calculatinga second estimated period of time when a request message for thehandover registration is transmitted from the mobile communicationterminal to the corresponding node via the second access network;determining a point in time of completing the handover registrationaccording to the first estimated period of time and the second estimatedperiod of time; and releasing an association with the first accessnetwork after the point in time of completing the handover registration.7. The method of claim 6, wherein the determining determines the pointin time of completing the handover is the sum of the first estimatedperiod of time and the second estimated period of time, and a startingpoint in time is established as a point in time of transmitting therequest message to a corresponding node (CN) via the AN1.
 8. Anon-transitory computer-readable recording medium storing a program forimplementing a method of providing a handover service to a mobilecommunication terminal supporting multi-modal communications, the methodcomprising: transmitting and receiving data to/from a corresponding nodevia a first access network and a second access network whilesimultaneously maintaining an association with the first access networkand the second access network; determining a point in time of completinga handover registration; and releasing an association with the firstaccess network after the point in time of completing the handoverregistration, wherein the determining comprises transmitting a requestmessage for the handover registration to the corresponding node via thesecond access network, receiving, via the first access network, acompletion message of the handover registration from the correspondingnode in response to receiving the request message for the handoverregistration, and determining the point in time of receiving thecompletion message of the handover registration as the substantiallysame point in time of completing the handover registration.
 9. Anon-transitory computer-readable recording medium storing a program forimplementing a method of providing a handover service to a mobilecommunication terminal supporting multi-modal communications, the methodcomprising: transmitting and receiving data to/from a corresponding nodevia a first access network and a second access network whilesimultaneously maintaining an association with the first access networkand the second access network; calculating a first estimated period oftime when a response message to a request for the handover registrationis transmitted from the corresponding node to the mobile communicationterminal via the first access network; calculating a second estimatedperiod of time when a request message for the handover registration istransmitted from the mobile communication terminal to the correspondingnode via the second access network; determining the point in time ofcompleting the handover registration according to the first estimatedperiod of time and the second estimated period of time; and releasing anassociation with the first access network after the point in time ofcompleting the handover registration.